Bearing material

ABSTRACT

A bearing material comprising a steel back metal, a porous layer of sintered copper or copper alloy, and a layer of an impregnated and sintered mixture filling the voids of said porous layer and forming a surface layer of the bearing material, said sintered mixture consisting of polytetrafluoroethylene, lead or lead oxide and graphite or a mixture of PTFE, lead fluoride and graphite.

United States Patent Morisaki [451 Dec. 12,1972

Japan [73] Assignee: Daido Metal Company Ltd.,

Nagoya, Japan 22 Filed: July 16,1971

21 App1.No.: 163,250

[301 Foreign Application Priority Data Oct. 27, 1970 Japan ..45/94498[52] US. Cl ..29/l82.3, 29/195, 75/208 R, 252/ 12 [51] Int. Cl. ..B22t7/00 [58] Field of Search ..75/208 R; 29/l82.3, 195; 252/12 [56]References Cited UNITED STATES PATENTS 3,553,806 1/1971 Turk et a1...75/208 R 3,518,186 6/1970 Andrews et a1 3,461,069 8/1969 Waldhuter eta1... 3,305,325 2/1967 Brasse et a1. 3,234,128 2/1966 McLeish et al..252/12 3,218,255 11/1965 Pratt ..252/12 3,142,559 7/1964 Rup et a1...29/l82.3 X 3,145,101 8/1964 Franssen ..29/l82.3 X 3,122,505 2/1964Rulon-Miller et a1. ..252/12 3,081,196 3/1963 MacDonald ..252/122,995,462 8/1961 Mitchell et a1 ..252/12 X 2,689,380 9/1954 Tait..75/208 R X 2,191,460 2/1940 Fisher ..75/208 R X FOREIGN PATENTS ORAPPLICATIONS 705,005 3/1954 Great Britain ..75/208 R 657,085 9/1951Great Britain ..75/208 R 3 Primary Examiner-Car1 D. Quarforth AssistantExaminer-R. E. Schafer Attorney-Karl W. Flocks [5 7] ABSTRACT A bearingmaterial comprising a steel back metal, a porous-layer of sinteredcopper or copper alloy, and a layer of an impregnated and sinteredmixture filling the voids of said porous layer and forming a surfacelayer of the bearing material, said sintered mixture consisting ofpolytetrafluoroethylene, lead or lead oxide and graphite or a mixture ofPTFE, lead fluoride and graphite.

2 Claims, 4 Drawing Figures PETENTED DEC 12 1912 1 sum 1 w 2 FIG. 2

BEARING MATERIAL This invention relates to a completely oilless bearingmaterial having low friction coefficient and excellent wear resistance.

The bearing material according to the invention comprises a steel backmetal, a porous layer of sintered I bronze formed on the surface of saidsteel back metal,

and a layer of a mixture of polytetrafluoroethylene (hereinafterabbreviated as PTFE), lead or lead oxide and graphite or a mixture ofPTFE, lead fluoride (PbF,)-and graphite applied to the surface of saidporous layer in the form of paste and then sintered thereon. It will beobvious that a conventionally used solid lubricant, such as molybdenumdisulfide (MOS,)

or tungsten disulfide (WS which have beencommonly used with good resultsin various fields of industry, can be used instead of graphite and purecopper or copper alloys can be used instead of bronze, in the subjectbearing material.

Now, the structure and the performances test results of the bearingaccording to the present invention will be described by way of examplewith reference to the accompanying drawing. In the drawing,

FIGS. 1 and 2 are 100x optical microphotographic pictures picturesrespectively showing the structures of the bearing materials accordingto the present invention; and

FIGS. 3 and 4 are graphic representations respectively showing theresults of the frictional abrasion tests conducted on the respectivebearing materials. Referring to FIGS. 1 and 2, reference symbol Adesignates a steel back metal layer (a low carbon steel containing about0.1 percent C), B a copper plating layer formed on the surface of saidsteel back metal layer, C a porous layer of sintered bronze overlayingsaid layer B (in practice, the interspace of the white spherical bronzeis filled with a black-colored filling material which is a mixtureconsisting of 80 percent by volume of PTFE and 20 percent by volume ofgraphite in FIG. 1 or a mixture consisting of 80 percent by volume ofPTFE, percent by volume of lead fluoride and 10 percent by volume ofgraphite in FIG. 2), D a surface layer of the same material as theaforesaid black-colored filling material, and E a resin layer which isusually used in the optical microphotographic inspection of metalstructures. FIG. 3 is a diagram graphically showing the relationshipsbetween the friction coefficient and the amount of wear, and theconcentrations of graphite and lead in the filling material and thesurface layer which are percent by volume in total of said fillingmaterial and surface layer. It will be understood from this diagram thatthe wear resistance (a curve B) and the friction coefficient (a curve A)are improved as the concentration of graphite increases. The results ofa number of experiments have revealed that the best result can beobtained when the filling material and the surface layer is composed of3-30 percent by volume of graphite, 0-25 percent by volume of lead orlead oxide and the remainder of PTFE, the total amount of graphite andlead or lead oxide being 3-40 percent by volume. It has been confirmedthat a total amount of these ingredients exceeding 40 percent by volumewill result in insufficient bonding strength between copper or copperalloy and the filling material, and hence a degradation of performanceof the product bearing.

FIG. 4 is a diagram graphically showing the relationships between thefriction coefficient and the amount of wear, and the concentrations ofgraphite and lead fluoride in the filling material and the surface layerconsisting of a mixture of PTFE, lead fluoride and graphite, the totalamount of said graphite and lead fluoride being 20 percent by volume.From this diagram, it will be seen that when the filling material andsurface layer consist of a mixture percent by volume of PTFE, 10 byvolume of lead fluoride and 10 percent by volume of graphite, thefriction coefficient (a curve C) of said filling material and surfacelayer is lowest and the amount of wear (a curve D) thereof tends tobecome somewhat smaller than the other compositions, though notsubstantially different from that of the latter. Based on the aboveexperimental results, the best result can be obtained when the fillingmaterial and the surface layer is composed of 3-30 percent by volume oflead fluoride, 0-30 percent by volume of graphite and the remainder ofPTFE, the total amount of graphite and lead fluoride being 3-40 percentby volume. It has been confirmed that a total amount of theseingredients exceeding 40 percent by volume will result in aninsufficient bonding strength between copper or copper alloy and thefilling material, and hence a degradation of performance of the producthearing.

The testing conditions employed in FIGS. 3 and 4 are as follows:

Tester: Suzuki's frictional abrasion tester Friction velocity: 0.036m/min Pressure applied: kg/cm' Test period: 60 min Lubrication: nonetemperature Room temperature The purity and grain size (mesh) of thegraphite used are about 84 percent and 600 mesh respectively in FIG. 3and about 95.5 percent and 280 mesh respectively in FIG. 4. Thethickness of the surface layer is 0.05 mm in FIG. 3 and 0.02-0.03 mm inFIG. 4.

Thus, it will be understood that a slight difference occurs in theexperimental result depending upon the quality of graphite and thethickness of the surface layer. For instance, while the frictioncoefficient of the surface layer of the material of FIG. 3 representedby the curve A should theoretically be the same as that of the surfacelayer of the material of FIG. 4 represented by the curve C, at the pointwhere the concentration of I ference therebetween. This may beattributable mainly to the difference in thickness of the surface layerand the difference in quality of graphite, particularly to thedifference in quality of graphite, although such difference probablyinvolves a minor measuring error.

As described hereinabove, the bearing material of the invention is anexcellent completely oilless bearing material having both low frictioncoefficient and high wear resistance which are most essential for theperforrnance of product bearings.

I claim:

1. A hearing material comprising a back metal consisting of a bandsteel, a porous layer of sintered copper or copper alloy overlying saidback metal, and a layer of a sintered mixture filling the voids of saidporous layer and forming a surface layer of the bearing material, saidsintered mixture consisting of 3-30 percent by volume of graphite, 0-25percent by volume of lead or lead oxide and the remainder ofsubstantially polytetrafluoroethylene, and the total amount of saidgraphite and said lead or lead oxide being 3-40 percent by volume.

2. A bearing material comprising a back metal consisting of a bandsteel, a porous layer of sintered copper or copper alloy overlying saidback metal, and a layer of sintered mixture filling the voids of saidporous layer and forming a surface layer of the bearing material,

said sintered mixture consisting of 3-30 percent by volume of leadfluoride, 0-30 percent of graphite and the remainder of substantiallypolytetrafluoroethylene, and the total amount of said lead fluoride andsaid graphite being 3-40 percent by volume.

2. A bearing material comprising a back metal consisting of a bandsteel, a porous layer of sintered copper or copper alloy overlying saidback metal, and a layer of sintered mixture filling the voids of saidporous layer and forming a surface layer of the bearing material, saidsintered mixture consisting of 3- 30 percent by volume of lead fluoride,0- 30 percent of graphite and the remainder of substantiallypolytetrafluoroethylene, and the total amount of said lead fluoride andsaid graphite being 3- 40 percent by volume.